Setup for hypernuclear gamma-ray Setup for hypernuclear gamma-ray spectroscopy spectroscopy

at the J-PARC K1.8 beam lineat the J-PARC K1.8 beam line

Department of Physics, Tohoku Univ.

K. Shirotori　for the Hyperball-J collaboration

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ContentsContents Introduction Magnetic spectrometer : SksMinusMagnetic spectrometer : SksMinus -ray detector array : Hyperball-J-ray detector array : Hyperball-J SummarySummary

IntroductionIntroduction

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E13 Day-1 experiment at E13 Day-1 experiment at J-PARCJ-PARCSeveral light hypernuclear -ray spectroscopy experiments are planned.

(4He, 7

Li, 10B, 11

B, 19F )

(K(K--, , - - ) reaction @ p) reaction @ pKK = 1.5 GeV/c = 1.5 GeV/c

Hyperball-J

Missing mass analysisMissing mass analysis -ray measurement-ray measurement

Optimized magnetic spectrometer + Hyperball-JOptimized magnetic spectrometer + Hyperball-J

Particle-Particle- coincidence coincidence

Magnetic Magnetic spectrometer spectrometer -SksMinus--SksMinus-

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Momentum resolution0.1%FWHM (0.72 MeV/c)

@ 720 MeV/c, 2.2T

Acceptance 100 msr @ 0.72GeV/c

Maximum central momentum

1.0 GeV/c @ 2.7T

1.05 GeV/c (+, K+) reaction (K+ 0.72 GeV/c)

2.2T

scat~20°

Previous SKS setupPrevious SKS setup Incident beam directionIncident beam direction Size and placement of Size and placement of detectors at the exit of the detectors at the exit of the SKS magnetSKS magnet

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Momentum resolution0.1%FWHM (0.72 MeV/c)

@ 720 MeV/c, 2.2T

Acceptance 100 msr @ 0.72GeV/c

Maximum central momentum

1.0 GeV/c @ 2.7T

1.05 GeV/c (+, K+) reaction (K+ 0.72 GeV/c)

scat~20°

Previous SKS setupPrevious SKS setup Incident beam directionIncident beam direction Size and placement of Size and placement of detectors at the exit of the detectors at the exit of the SKS magnetSKS magnet

2.7T

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Momentum resolution0.1%FWHM (0.72 MeV/c)

@ 720 MeV/c, 2.2T

Acceptance 100 msr @ 0.72GeV/c

Maximum central momentum

1.0 GeV/c @ 2.7T

1.05 GeV/c (+, K+) reaction (K+ 0.72 GeV/c)

scat~20°

SksMinus setupSksMinus setupFor the beam condition Determination of incident beam angle (20 degree) Larger drift chamber

2.7T

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SksMinus setupSksMinus setup

SDC1~4 : Drift chambersSDC1~4 : Drift chambers

STOF : TOF counterSTOF : TOF counter

SAC : Aerogel Cherenkov counterSAC : Aerogel Cherenkov counter

Beam decay background vetoBeam decay background veto SMF : SMF : -- from K from K- - → → - - + + SP0 : SP0 : -- from K from K- - → → - - + + 00

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Target ~20 g/cmTarget ~20 g/cm22

1 m

RequirementsRequirements Acceptance >100 msr, ~20Acceptance >100 msr, ~20oo scattering angles scattering angles Momentum resolution < 4 MeV/c (FWHM)Momentum resolution < 4 MeV/c (FWHM)

(K(K--, , - - ) reaction @ p) reaction @ pKK = 1.5 GeV/c Analyze 1.4 GeV/c ⇒ = 1.5 GeV/c Analyze 1.4 GeV/c ⇒ --

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Drift chamber and TOF Drift chamber and TOF countercounter

170 cm

270 cm

BD1 BD2

48D48 Magnet

Ajimura-san

BT

BD and BT from BNL are used as BD and BT from BNL are used as SDC3&4 and STOF, respectively.SDC3&4 and STOF, respectively.BDBD

BNL-AGS D6 lineBNL-AGS D6 line

To keep the large acceptanceTo keep the large acceptance

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Simulation results of Simulation results of acceptance and momentum acceptance and momentum resolutionresolution

Acceptance at 1.4 GeV/c, Acceptance at 1.4 GeV/c, ~130 msr~130 msr Enough angular acceptance,Enough angular acceptance, ~~20 degree20 degree Momentum resolution at 1.4 GeV/c Momentum resolution at 1.4 GeV/c ~2.1 MeV/c (FWHM)~2.1 MeV/c (FWHM)

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Beam K

BAC SACTarget20cm

Decay

Background events : Beam Background events : Beam decaydecay

KK- - → → -- (63.4%) (63.4%)

⇒ ⇒Muon FilterMuon FilterKK- - → → - - 00 (21.1%) (21.1%)

⇒ ⇒PiZero VetoPiZero Veto

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Trigger rateTrigger rate Missing massMissing mass

Overlap

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Beam decay veto countersBeam decay veto counters

86%86% of of events detected events detectedOthers rejected (stopped in the Others rejected (stopped in the iron) by offline analysis iron) by offline analysis Totally Totally > 99.9 %> 99.9 % Over kill for true π Over kill for true π ~2.5%~2.5%

80%80% of of --00 events detected events detected10 sets10 sets of 3 mm lead plate of 3 mm lead plate and 8 mm scintillation and 8 mm scintillation counter layercounter layer at 1.5 GeV/c at 1.5 GeV/c beam.beam.

- (passing through)

- (absorbed in the iron)

Sufficient performance to reduce the trigger rate and backgroundSufficient performance to reduce the trigger rate and background

Muon Filter

Hyperball-JHyperball-J

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Hyperball-JHyperball-J

Hyperball-J (half)

Mechanical coolerMechanical cooler PWO background suppressorPWO background suppressor Waveform readoutWaveform readout

~6%~6% photo peak efficiency @ 1 MeV photo peak efficiency @ 1 MeV

Severe radiation damageSevere radiation damageHigh counting rateHigh counting rate

Simulated efficiency by Geant4Simulated efficiency by Geant4

at J-PARCat J-PARC

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New Ge detector with New Ge detector with Mechanical coolingMechanical cooling

R&D in KEK and Tohoku Univ. Cooling power

Ge crystal temperature less than 85K when biased Low mechanical vibration for 2 keV energy resolution

Minimization of microphonics noise

Mechanical coolerMechanical cooler⇒⇒Suppression of the radiation damage effect with Ge crystal below Suppression of the radiation damage effect with Ge crystal below 8585 K K(Liquid nitrogen cooling ~90 K)(Liquid nitrogen cooling ~90 K)

AchievedAchieved

GeGeCoolerCooler10 cm10 cm

13 cm13 cm

Ge

Compressor

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Background suppressor : Background suppressor : PPbbWOWO44

Doped PWO crystalDoped PWO crystal Cooling of PWO below 0℃Cooling of PWO below 0℃

W-type

U-type

L-type

-type

PWO suppression for PWO suppression for ray spectroscopy is possible. ray spectroscopy is possible.

The PWO crystal has very first decay constant ~6 ns. The PWO crystal has very first decay constant ~6 ns. (~300 ns for BGO)(~300 ns for BGO)But But small light yieldsmall light yield (PWO/BGO=1/10) (PWO/BGO=1/10)

Ge energy spectrumGe energy spectrum1 MeV 1 MeV ray (simulation) ray (simulation)

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Waveform readoutWaveform readoutTo improve energy resolution To improve energy resolution

and recover rejected events and recover rejected events

at high counting ratesat high counting rates Baseline shift restorationBaseline shift restoration Pile-up signal decompositionPile-up signal decomposition

Pulse height ADCPulse height ADC ⇒ ⇒ Sampling ADCSampling ADC

(waveform digitization)(waveform digitization)(after shaping)(after shaping)

10 V

Preamp outputPreamp output After shapingAfter shaping

BaselineBaseline

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Waveform readoutWaveform readoutTo improve energy resolution To improve energy resolution

and recover rejected events and recover rejected events

at high counting ratesat high counting rates Baseline shift restorationBaseline shift restoration Pile-up signal decompositionPile-up signal decomposition

Pulse height ADCPulse height ADC ⇒ ⇒ Sampling ADCSampling ADC

(waveform digitization)(waveform digitization)(after shaping)(after shaping)

In the LNS test experiment, the In the LNS test experiment, the positron beam is irradiated to Ge positron beam is irradiated to Ge detector to make frequent baseline detector to make frequent baseline shits by reset signal.shits by reset signal.⇒⇒The restoration of the baseline shitsThe restoration of the baseline shits

3.7 keV⇒3.7 keV⇒ 3.1 keV (FWHM) 3.1 keV (FWHM)(2.6 keV w/o beam)(2.6 keV w/o beam)

No baseline restorationNo baseline restoration

Baseline restorationBaseline restoration

6060Co 1.3 MeV Co 1.3 MeV -ray spectrum-ray spectrum

SummarySummary

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SummarySummary J-PARC E13 experiment by the (KJ-PARC E13 experiment by the (K--, , --) reaction @ p) reaction @ pKK =1.5 GeV/c =1.5 GeV/c

• Optimal magnetic spectrometerOptimal magnetic spectrometer• New Hyperball system for the high counting rateNew Hyperball system for the high counting rate

Magnetic spectrometer, Magnetic spectrometer, SksMinusSksMinus and newly constructed array, and newly constructed array, Hyperball-JHyperball-J

SksMinus performanceSksMinus performance• More than 100 msr acceptance and 20 degree coverageMore than 100 msr acceptance and 20 degree coverage• ~2 MeV/c momentum resolution~2 MeV/c momentum resolution

Hyperball-J Hyperball-J • ~6 % efficiency~6 % efficiency• Mechanical cooling system Mechanical cooling system • PWO counterPWO counter• Waveform readoutWaveform readout

The experiment will be performed in 2009. The experiment will be performed in 2009.

BackupBackup

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Particle identificationParticle identification

Rejection of KRejection of K-- beam through beam through backgroundbackgroundSAC ~98% + Beam veto (SFV)SAC ~98% + Beam veto (SFV)STOF : Time resolution ~150 ps (rms)STOF : Time resolution ~150 ps (rms)

SAC

Beam veto (SFV)

Reaction ID by BAC and SAC (n=1.03) @ triggerReaction ID by BAC and SAC (n=1.03) @ trigger

BAC

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(K(K--, , --) reaction) reactionLarge production rate (/beam)Large production rate (/beam)

Large elementary cross section, n(KLarge elementary cross section, n(K--, , --)) : : order of mb order of mb

> n(> n(++, K, K++)) : ~10 : ~1022 b, p(e, e’Kb, p(e, e’K++)) : ~1 : ~1 bb

Large sticking probabilityLarge sticking probability

More advantages in hypernuclear More advantages in hypernuclear -ray spectroscopy -ray spectroscopy experimentexperiment

Angular selectivity Angular selectivity

Small momentum transferSmall momentum transfer

5°~ 100 MeV/c : 5°~ 100 MeV/c : L = 0L = 0

10°~ 200 MeV/c : 10°~ 200 MeV/c : L = 1 or 2 @ 1.5 GeV/c beamL = 1 or 2 @ 1.5 GeV/c beam

Spin-flip cross sectionSpin-flip cross section exists at large angles ( exists at large angles (>10°).>10°).